This invention relates to a method and apparatus for measuring the position of a vibrating object. Specifically, the invention is applied to the field of ring-laser gyroscopes.
In many instances, it is desirable to know the position of a vibrating object relative to some reference point. Particularly, in a ring-laser gyroscope the sensing element ("gyro block") is dithered, i.e. forced into angular vibration in order to overcome the effect of "lock in". The amplitude of angular vibration can be of the order of 100 arc seconds. In some inertial navigation applications, it may be necessary to have an accurate knowledge of the position of the block as it is dithered relative to the case of the instrument to an accuracy of several arc seconds
In a single-axis ring-laser gyro, the position of the block relative to the case is inferred by optical means in which the motion of the block relative to the case is subtracted from the total indicated motion of the gyro so that the read out is only the motion of the case of the gyro in inertial space. This technique is known as "optical compensation" and requires the use of optical components such as combiner prisms which are expensive to fabricate and difficult to adjust.
Optical compensation of a monolithic, three-axis ring-laser gyro is even more problematic than that of the single-axis gyro. Therefore, the desirability of achieving the same result as optical compensation by electronic means has been widely recognized.